a) Technical Field of the Invention
The present invention relates to a device for enhancing the linear polarization intensity of light which passes through a polarizer, which is used in liquid crystal display or polymer dispersed liquid crystal display employed in watch display or automatic display.
b) Description of the Prior Art
Conventionally, polarizers are substantially divided into three categories. The first category employs the principle of anisotropic absorption of light, for instance, polymer of anisotropic absorption of light being used to form a polarizer. The second category employs the principle of anisotropic refraction of light, for example, Wollaston prism. The third category employs the principle of anisotropic reflection of light, for example, Glan-Foucault prism. After the natural light enters these three kinds of polarizers, the intensity of the polarized light emitted from the polarizer is smaller than half of the intensity of the originally incident natural light.
In the structure of common liquid crystal display, the polarizer is an essential optical element. As a result of the application of the polarizer, the light source loses half of its energy. In order to improve the drawback, a polarizing beam splitter is used to split the natural light into two polarized light beams, i.e., right circularly polarized light and left circularly polarized light. Subsequently, polarization characteristics of the two polarized light beams are changed and then the two polarized light beams are combined again. In view of this, the efficiency of utilization of light source can be improved. However, the volume, weight and size of the liquid crystal display are increased. Therefore, the liquid crystal display has lost its advantages of thin in thickness, light in weight, and small in size. Accordingly, it is essential to solve the problem by enhancing the light transmissivity of the polarizer.
In addition, for instance, the polymer dispersed liquid crystal display, employs the effect of light scattering to improve viewing angle characteristics and enhance light transmissivity. If alignment treatment is performed on the polymer and liquid crystal of the polymer dispersed liquid crystal display, the scattering efficiency of the display can be improved. However, the scattering characteristics after alignment treatment are related to polarization direction of light. Therefore, for an incident natural light, one may hope to change the equally distributed polarization state into an anisotropically distributed polarization state such as to promote the diffraction efficiency for the aligned polymer dispersed liquid crystal.
Accordingly, an object of the present invention is to provide a device for enhancing the linear polarized light intensity which passes through a linear polarizer. The present invention employs a prepolarizer to receive the incident natural light. The incident natural light is converted into multiple beams having relatively significant polarization direction. The multiple beams then pass through a polarizer to obtain a linearly polarized light having high light transmissivity. In view of this, the liquid crystal display has the advantages of thin in thickness, light in weight and small in size.
Another object of the present invention is to provide a device for enhancing the linear polarized light intensity which passes through a linear polarizer, wherein the prepolarizer can change the polarization of the incident natural light under the condition that the intensity of the synthesized light is almost unaffected. Therefore, the prepolarizer can be mounted on the polymer dispersed liquid crystal display. In this way, not only the scattering efficiency of the liquid crystal display can be enhanced, but also the high brightness characteristic of the polymer dispersed liquid crystal display can be maintained.
One aspect of the present invention is to provide a device for enhancing the linear polarized light intensity which passes through a linear polarizer, which comprises: a prepolarizer receiving incident natural light and splitting the natural light into a plurality of polarized light beams with different polarization directions, changing the polarization direction of the light beams, thereby enhancing the total light intensity of a particular polarization direction; and a polarizer having polarization direction the same as that of the prepolarizer, receiving the light emitted from the prepolarizer and converting the emitted light into a linear polarized light.
The prepolarizer can be a layer composed of a cholesteric liquid crystal; and the layer is sandwiched between two transparent plates wherein finger print texture is formed, such that grating effect and optically active effect are generated for the incident natural light.
The prepolarizer can be a device that comprises: (1) a layer of prism set made of uniaxial briefringent material for splitting the incident natural light into two kinds of light beams, ordinary light and extra-ordinary light in different propagating direction. (2) film made of optically active material for changing the polarization direction of the two kinds of light beams, thereby enhancing the transmitted light intensity of a particular polarization direction.
Besides, the prepolarizer can be a transparent solid state polymer layer having optical activity, wherein finger print structure is formed. The transparent solid state polymer layer provides grating effect and optically active effect for the incident light.
Furthermore, the prepolarizer can be an UV-curable polymer dispersed liquid crystal layer having optical activity, wherein UV interference pattern is employed to project on the layer to form grating effect and optically active effect.
Another object of the present invention is to provide a device for enhancing the linear polarization intensity of light which passes through a polarizer, which comprises: (a) a plurality of superimposed prepolarizers, each having different period, which receive incident natural light and splitting the natural light into a plurality of polarized light beams with different polarization directions, changing the polarization direction of the light beams, thereby enhancing the light intensity of a particular polarization direction, eliminating the color effect caused by unequal birefringent and optical activity of incident light beams of different colors; and (b) a polarizer having polarization direction the same as that of the prepolarizer, receiving the light emitted from the prepolarizer, and then converting the emitted light into a linearly polarized light.
In addition, UV interference pattern can be employed to project on UV-curable polymer dispersed liquid crystal having optical activity multiple times to mitigate color effect.